Digital FM stereo receiver architecture

Abstract

Systems and techniques for digital processing of FM stereo signals are described. According to an aspect, a method includes determining whether a received digital signal is a mono signal or a stereo signal, using a digital signal processor to process the received digital signal based on stereo transmission when the received digital signal is determined to be a stereo signal, and using the same digital signal processor to process the received digital signal based on mono transmission when the received digital signal is determined to be a mono signal.

What is claimed is: 
     
       1. A method comprising:
 determining whether a received digital signal is a mono signal or a stereo signal; 
 using a digital signal processor to process the received digital signal based on stereo transmission when the received digital signal is determined to be a stereo signal; and 
 using the same digital signal processor to process the received digital signal based on mono transmission when the received digital signal is determined to be a mono signal. 
 
     
     
       2. The method of  claim 1 , comprising filtering and sub-sampling the received digital signal using the digital signal processor. 
     
     
       3. The method of  claim 1 , comprising filtering, sub-sampling and de-emphasizing the received digital signal using the digital signal processor. 
     
     
       4. The method of  claim 1 , comprising:
 using a left/right processor, which is coupled with an output of the digital signal processor, to generate a separate left bitstream and right bitstream based on an output signal from the digital signal processor when the received digital signal is determined to be a stereo signal; and 
 bypassing the left/right processor when the received digital signal is determined to be a mono signal. 
 
     
     
       5. The method of  claim 4 , wherein the left/right processor comprises two summers coupled with an input of the left/right processor. 
     
     
       6. The method of  claim 1 , wherein using the digital signal processor to process the received digital signal based on stereo transmission comprises using two instances of the same digital signal processor to handle L+R and L−R processing in parallel. 
     
     
       7. The method of  claim 1 , wherein determining whether the received digital signal is a mono signal or a stereo signal comprises filtering the received digital signal to produce a filtered signal. 
     
     
       8. The method of  claim 7 , wherein determining whether the received digital signal is a mono signal or a stereo signal comprises comparing an amplitude of the filtered signal with a reference amount. 
     
     
       9. The method of  claim 1 , comprising:
 down-sampling the received digital signal before determining whether the received digital signal is a mono signal or a stereo signal; 
 providing the down-sampled digital signal to the digital signal processor when the down-sampled digital signal is determined to be a mono signal; and 
 when the down-sampled digital signal is determined to be a stereo signal, recovering a carrier signal based on the down-sampled digital signal and providing to the digital signal processor a digital signal generated by multiplication with the carrier signal. 
 
     
     
       10. A method comprising:
 receiving a digital signal based on a received mono signal or a received stereo signal; 
 bandpass filtering the received digital signal to obtain a pilot signal; 
 detecting the pilot signal when a magnitude of the bandpass filtered signal is greater than a predetermined threshold; and 
 filtering and processing the received digital signal based on stereo transmission, including recovering a carrier signal based on the digital signal, when the pilot signal is detected. 
 
     
     
       11. The method of  claim 10 , comprising filtering and processing the received digital signal based on mono transmission when the pilot signal is not detected. 
     
     
       12. The method of  claim 10 , wherein recovering the carrier signal based on the digital signal comprises using the pilot signal detected from the bandpass filtering. 
     
     
       13. A non-transitory computer readable medium storing a computer program configured to cause a frequency modulation (FM) stereo demodulator system to perform operations comprising:
 determining whether a received digital signal is a mono signal or a stereo signal; 
 using a digital signal processor to process the received digital signal based on stereo transmission when the received digital signal is determined to be a stereo signal; and 
 using the same digital signal processor to process the received digital signal based on mono transmission when the received digital signal is determined to be a mono signal. 
 
     
     
       14. The non-transitory computer readable medium of  claim 13 ,
 the operations comprising filtering and sub-sampling the received digital signal using the digital signal processor. 
 
     
     
       15. The non-transitory computer readable medium of  claim 13 ,
 the operations comprising filtering, sub-sampling and de-emphasizing the received digital signal using the digital signal processor. 
 
     
     
       16. The non-transitory computer readable medium of  claim 13 , the operations comprising:
 using a left/right processor to generate a separate left bitstream and right bitstream based on an output signal from the digital signal processor when the received digital signal is determined to be a stereo signal. 
 
     
     
       17. The non-transitory computer readable medium of  claim 13 ,
 wherein using the digital signal processor to process the received digital signal based on stereo transmission comprises using two instances of the same digital signal processor to handle L+R and L−R processing in parallel. 
 
     
     
       18. The non-transitory computer readable medium of  claim 13 ,
 wherein determining whether the received digital signal is a mono signal or a stereo signal comprises filtering the received digital signal to produce a filtered signal. 
 
     
     
       19. The non-transitory computer readable medium of  claim 18 ,
 wherein determining whether the received digital signal is a mono signal or a stereo signal comprises comparing an amplitude of the filtered signal with a reference amount. 
 
     
     
       20. The non-transitory computer readable medium of  claim 13 , the operations comprising:
 down-sampling the received digital signal before determining whether the received digital signal is a mono signal or a stereo signal; 
 providing the down-sampled digital signal to the digital signal processor when the down-sampled digital signal is determined to be a mono signal; and 
 when the down-sampled digital signal is determined to be a stereo signal, recovering a carrier signal based on the down-sampled digital signal and providing to the digital signal processor a digital signal generated by multiplication with the carrier signal. 
 
     
     
       21. A non-transitory computer readable medium storing a computer program configured to cause a frequency modulation (FM) stereo demodulator system to perform operations comprising:
 receiving a digital signal based on a received mono signal or a received stereo signal; 
 bandpass filtering the received digital signal to obtain a pilot signal; 
 detecting the pilot signal when a magnitude of the bandpass filtered signal is greater than a predetermined threshold; and 
 filtering and processing the received digital signal based on stereo transmission, including recovering a carrier signal based on the digital signal, when the pilot signal is detected. 
 
     
     
       22. The non-transitory computer readable medium of  claim 21 , wherein the operations comprise filtering and processing the received digital signal based on mono transmission when the pilot signal is not detected. 
     
     
       23. The non-transitory computer readable medium of  claim 21 , wherein recovering the carrier signal based on the digital signal comprises using the pilot signal detected from the bandpass filtering.